The present invention relates to an organic-inorganic composite as a cathode material for a secondary lithium battery and a method for manufacturing the same, and, more particularly, to an organic-inorganic composite as a cathode material for a secondary lithium battery in which two different organic polymers are stabilized between V2O5 layers by intercalation and a method for manufacturing the same.
A secondary lithium battery is an energy storage device being capable of charging and discharging, which is widely used as a power source of small and/or portable electrical devices such as cellular phone, laptop computer and mobile telecommunication. Recently, development of the secondary battery that is lighter and has higher charge/discharge capacity is one of major issues. Secondary lithium battery comprises a cathode, an electrolyte and a negative electrode, in which charge/discharge characteristic of cathode material is one of most important factors to determine the capacity for energy storage in secondary lithium battery.
As for the cathode materials in secondary lithium battery, crystalline cobalt-, manganese- and nickel-based oxides are the most studied materials. Commercialized LiCoO2 has high reduction-oxidation potential along with long term stability, but it has disadvantages of high cost and low charge/discharge capacity. In case of Li2Mn2O4, it has been considered as an alternative to conventional LiCoO2 because of low cost, but it has still problem in terms of charge/discharge capacity and long term stability. For the case of LiNiO2, although it is better in theoretical discharge capacity than LiCoO2 it has a difficulty in preparation. Therefore, there is a demand for a new electrode material to overcome the shortcomings of the crystalline transition metal oxides as described above.
Recent trends in the field of portable electrical devices for telecommunications are also on going to reduce power consumption, which requires a relatively low working voltage together with high energy density. To meet this end, the secondary battery with high charge/discharge capacity is required. Therefore, an attempt of synthesizing amorphous type, nano-particle and organic-inorganic compounds has been made to improve charge/discharge capacity.
Xerogel and/or aerogel type V2O5 is proved to be a good material for cathode in secondary lithium battery, much better in lithium insertion/extraction performance than crystalline phase, by Smyrl group of Minnesota University. In particular, the two dimensional structure of V2O5 allows organic molecules or ions to be intercalated into the V2O5 layers. Recently, improved discharge capacity for electrochemical lithium insertion has been observed for the oxygen post-treated polyaniline (PANI)-intercalated V2O5 nanocomposites, which is disclosed by Nazar group in Canada and Gomez-Romero group in Spain (xe2x80x9cAn organic-inorganic polyaniline/V2O5 systemxe2x80x9d, The Journal of Electrochemical Society, vol. 146, no. 6, pp2029-2033, 1999.
In addition to the metal oxide-based electrode materials, organic materials can be utilized as a cathode in secondary lithium battery. An example is the 2,5-dimercapto-1,3,4-thiadiazole (DMcT)/PANI composite that demonstrates high discharge capacity of 185 mAh/g, which is reported by Oyama group in Japan (xe2x80x9cdimercapto-polyaniline composite electrode for a lithium battery of high energy densityxe2x80x9d, Nature, vol. 373, no. 6515, p598-800, 1995).
Therefore, it is an object of the present invention to provide a composite material for a cathode in secondary lithium battery with excellent charge/discharge characteristics and a method for manufacturing the same.
In accordance with an aspect of the present invention, there is provided an organic-inorganic composite for use as a cathode in a secondary lithium battery comprising a V2O5 xerogel in which poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT) and polyaniline are co-intercalated, where the nominal composition of V2O5, xerogel:PDMcT:PANI is preferably 1:0.2-1:0.2-2 in mole %.
In accordance with another aspect of the present invention, there is provided a method for manufacturing an organic-inorganic composite for use as a cathode in a secondary lithium battery, the method comprises the fllowing steps of: (a) preparing V2O5 xerogel powder; (b) dissolving the V2O5 xerogel powder in distilled water to form V2O5-water solution; (c) dissolving DMcT molecule in organic solvent to form DMcT solution; (d) adding slowly the V2O5-water solution to the DMcT solution; (e) adding aniline to the resultant of (d); (f) reacting the resultant of (e) for 24 hours at a room temperature and then filtering and washing; and (g) drying the resultant of (f), where drying temperature at the step (g) is ranging from the room temperature to 80xc2x0 C.
And, in accordance with still another aspect of the present invention, there is provided the manufacturing method after the step (g), further comprising the step of undergoing thermal treatment in an oxygen gas atmosphere, where the temperature and the heating time is 80 to 120xc2x0 C. and 3 to 10 hours, respectively.